The invention relates to a method for identifying interchangeable lenses that can be connected with the aid of a locking apparatus in a prescribed position to a support surface on a camera of a camera system, and to an apparatus for carrying out the method.
Methods for exchanging information between interchangeable lenses of a camera system that can be fitted with the aid of a locking apparatus, usually designed as a bayonet connection, onto a support surface on a system camera, for example a mirror reflex camera or a metering viewpoint camera, are known per se in the case of modern camera systems. In the case of older mechanical camera systems, by contrast, the lack of interfaces renders impossible the exchange of information. The interchangeable lenses of modern camera systems generally have electric consumers such as automatic focus and aperture control mechanisms. The bayonet connections therefore frequently have a number of electrical contacts. These electrical contacts are used, on the one hand, to supply power to the electric consumers in the lens and, on the other hand, for methods intended to transmit signals between lens and camera housing. In this way, a bidirectional data transmission from the camera housing to the lens is equally as possible as a data transmission from the lens to the camera. In the case of such methods for exchanging information, both lens setting information, such as the currently set range or working aperture, is transmitted to the camera, and so are basic lens data such as focal length and aperture ratio. If the lens has measurable systematic errors such as, for example, vignetting, coma or backfocus errors, these can be stored in a data memory in the lens and be transmitted to the camera electronics if required for correction purposes. However, such methods fundamentally require a multiplicity of electrical contacts which are frequently arranged tightly next to one another and are susceptible to interference. For example, when a lens is fitted onto the camera housing undesired electrical connections can come about between contacts that are not to be connected to one another. Contacting problems also frequently arise after the camera has not been used for some time.
To avoid these problems, it is known from EP 1 006 397 B1 to separate the signal transmission from the power supply by using optocouplers for contactless bidirectional optical signal transmission. Undesired short circuits between signal connections and power supply connections of the lens and of the camera housing when the lens is fitted in are reliably prevented in this way.
DE 34 38 322 A1 discloses a method for transmitting signal data between the lens and a camera of a camera system. On the camera side, a defined radiation is generated that has at least one of its properties varied in accordance with at least one mechanical manipulated variable, and is then converted into an electric signal that is used to display the manipulated variable and/or to control camera functions. It is possible in this way to transmit lens setting information from the lens to the camera. The defined radiation generated in the camera housing is firstly fed, with the aid of complicated optical means, for pickup and for guidance of the said radiation, to the lens, and subsequently returned to the camera housing. The lens has additional means for this purpose that varies at least one of the properties of the said radiation in accordance with at least one mechanical manipulated variable, and in this way enables the transmission of lens setting information. Means are provided in the camera housing for evaluation with regard to the display of this information and/or the control of camera functions. The arrangement requires a great deal of space and many individual components.
A further device with optical detection of signal data may be gathered from DE 34 43 443 A1. The relative movement between lens mount and camera body in relation to one another that necessarily occurs during fitting of the lens is used in order to be able to detect an optically readable scale in the form of a bar code on the pickup lens. The detection of the bar code is possible only during the fitting operation. Since the reading device must always be operationally ready precisely during the fitting operation, but this instant is not known, it is impossible to rule out malfunctions in the detection of the scale. The detection of a bar code of an already fitted lens, for example after the camera has been switched on, is impossible. The known methods cannot be used in the case of interchangeable lenses of relatively old mechanical camera systems, and existing lenses cannot be converted, or can be converted only with a high, uneconomic outlay.